Quantitative immunolocalization of a P29 protein (GRA7), a new antigen of Toxoplasma gondii

Ultrastructural localization of a P29 protein of Toxoplasma gondii was exam ined on thin sections by an immunogold technique using a P29 antigen-specif ic monoclonal antibody (5-241-178). Immunolocalization of the P29 protein i n extracellular tachyzoites demonstrated that this antigen was present in t he dense granules. Thus, we have identified this P29 antigen as the seventh protein (GRA7) to be localized to the dense granules of T. gondii. P29 imm unolocalization in intracellular tachyzoites demonstrated association of th is antigen with the parasite membrane complex, tubular elements of the intr avacuolar network, and with the parasitophorous vacuolar membrane. Our immu nolabeling data suggest trafficking of the P29 (GRA7) antigen from the dens e granule via the intravacuolar network to the parasitophorous vacuolar mem brane on invasion of the tachyzoite into the host cell.